1. Field of the Invention
The present invention is in the field of hypodermic syringes and more specifically relates to a type of hypodermic syringe that can be supplied in an empty condition, into which a fluid can be aspirated, and which can easily be rendered non-reusable after the first use.
2. The Prior Art
In a number of foreign countries mass immunization programs are being conducted to control certain diseases endemic to those countries. While this is highly desirable, the syringes used remain reusable after their intended use. Repeated use of these hypodermic needles is one of the major causes of the spread of more than 15 diseases including AIDS and hepatitis.
What is desperately needed is a fool-proof technique for rendering the syringes used for immunization non-reusable.
In U.S. Pat. No. 4,391,272 issued July 5, 1983 to Staempfli and in U.S. Pat. No. 4,233,975 issued Nov. 18, 1980 to Yerman there are shown various embodiments of syringes in which, typically, a barb on the plunger engages a groove in the cylindrical wall of the syringe to prevent the plunger from being retracted.
In these patents, the drive rod pulls out of the plunger if an attempt is made to retract the plunger after it has been placed in the latched position. This aspect raises doubts regarding the possibility of aspirating fluid into these syringes. Because the fluid being aspirated cannot flow rapidly through the small bore of the needle, any attempt to retract the plunger rapidly will be met by a substantial resistive force. This force might possibly dislodge the drive member from the plunger. Also, the drive rod could be glued back in place.
The present invention permits rapid aspiration of fluid into the syringe, and provides a different mechanism for latching the plunger after all of the contents of the syringe have been expressed, thereby rendering the syringe non-reusable.
In U.S. Pat. No. 3,941,129 Pleznac discloses that a stopper located in the bore of a syringe adjacent but not connected to the drive piston can be used to give an unalterable visual alert if the drive piston has been advanced in the cylinder prior to the intended use; i.e., if the syringe has been tampered with. The present invention improves on this syringe by providing means to render it non-reusable.